This application claims priority to U.S. provisional patent application No. 60/724,287, filed on Oct. 7, 2005, the contents of which are incorporated herein by reference. This application also claims priority to Japanese patent application no. 2005-197031, filed on Jul. 6, 2005, the contents of which are incorporated herein by reference.
A. Technical Field
The present invention relates to an exposure apparatus applicable to photolithography and particularly to an exposure apparatus for EUVL (EUVL: Extreme UltraViolet Lithography) in which the exposure wavelength is 50 nm or less.
B. Background Art
In common exposure apparatuses, a sensor for monitoring fluctuations in the quantity of light of the exposure light is built in (see Japanese Unexamined Patent Application Publication Nos. H9-36018 and H11-16816, etc.). In particular, Japanese Unexamined Patent Application Publication No. H9-36018 discloses a system (lens adjustment system) that arranges sensors at the upstream side and the downstream side of a projection optical system, estimates the amount of fluctuation in the characteristics of the projection optical system based on the output of those sensors, and adjusts the projection optical system so as to control this. It is preferable that this type of adjustment system also be built into exposure apparatuses for EUVL, which are the next generation of exposure apparatuses.
However, the inventors of the present invention have found that when this adjustment system is applied as-is to an exposure apparatus for EUVL, there is a possibility that the system will not operate properly. The reasons for this include the fact that a special light source for EUVL (EUV light source) is used in the exposure apparatus for EUVL and the fact that a special mirror for reflecting EUV light (multilayer film reflecting mirror) is used. In those cases, it is thought that it would be difficult to estimate the amount of fluctuation of the characteristics of the projection optical system from the fluctuation of the quantity of light of the exposure light.
Therefore, the purpose of the present invention is to provide an exposure apparatus, for example, an exposure apparatus for EUVL, that is able to accurately ascertain fluctuations in the characteristics of the optical system resulting from the irradiation heat of light.